Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $138.64   5.489%   $146.2499   $146.25   $146.25   $146.20  
  Purchase #2 $149.90   4.297%   $156.3412   $156.34   $156.35   $156.30  
  Purchase #3 $148.98   10.697%   $164.9164   $164.92   $164.90   $164.90  
  Purchase #4 $77.92   7.602%   $83.8435   $83.84   $83.85   $83.80  
  Purchase #5 $244.96   12.872%   $276.4913   $276.49   $276.50   $276.50  
  Purchase #6 $163.39   6.113%   $173.378   $173.38   $173.40   $173.40  
  Purchase #7 $193.36   4.421%   $201.9084   $201.91   $201.90   $201.90  
  7 purchase totals = $1,117.15       $1,203.1287   $1,203.13   $1,203.15   $1,203.00